1. Field of the Invention
The present invention relates to a method of fixing up a deteriorated site of the magneto-resistive effect device (reproducing device) in a thin-film magnetic head caused by the so-called thermal asperity occurring as a hard disk system is in operation, while that device remains incorporated in the hard disk system without dismantling it.
2. Explanation of the Prior Art
With recent improvements in the plane recording density of hard disk systems, there has been growing demands for improvements in the performance of thin-film magnetic heads. For the thin-film magnetic head, a composite type thin-film magnetic head has been widely used, which has a structure wherein a reproducing head having a read-only magneto-resistive effect device (hereinafter often referred to as the MR (magneto-resistive) device for short) and a recording head having a write-only induction type magnetic device are stacked on a substrate.
For the MR device, there is the mention of an AMR device harnessing an anisotropic magneto-resistive effect, a GMR device tapping a giant magneto-resistive effect, a TMR device making use of a tunnel-type magneto-resistive effect, and so on.
With regard to thin-film magnetic heads having various such magneto-resistive effect devices mounted on them, it has been reported that there is often the thermal asperity defect caused as an inherent one (see JP(A)2005-108306).
The thermal asperity is a phenomenon that occurs when a thin-film magnetic head passes over a magnetic disk plane that is a recording medium while levitating and flying over minute bumps or dents, because the magneto-resistive effect device is heated or cooled via the adiabatic compression and/or adiabatic expansion of air.
Of course, that phenomenon occurs not only in a non-contact state but also in a contact state where the magneto-resistive effect device is in contact with minute bumps or dents on the magnetic disk plane. When the head is in collision with minute asperities, there is a local, vigorous heating occurring due to mechanical vibrations and, at the same time, instantaneous friction. Such local heating is supposed to occur for a very short period in which the head passes over the asperities, and propagate right away to the whole device. When heat shocks propagate as if they were waves, the device is supposed to undergo repeated local expansion and local shrinkage.
How a typical deterioration by the thermal asperity occurs is now explained with reference to FIGS. 8A and 8B with an applied magnetic field as abscissa and the ensuing device resistance change as ordinate. Typical initial characteristics are shown in FIG. 8A. In the initial state with none of the deteriorations of the device, there is a linear resistance change vs. the applied magnetic field.
By contrast, FIG. 8B shows the characteristics of a device deteriorated by the thermal asperity while an HDD (hard disk drive system) is practically on the run. In FIG. 8B, there is a stepwise resistance change (kink) vs. the applied magnetic field. From the experience so far, it has been found that most of the deteriorations caused by the thermal asperity occur in this mode.
In a possible deterioration model (1), it would appear that a part of a bias magnetic field-applying layer is flipped over by heat shocks. A magneto-resistive effect film does not show any linearity in general, and a given magnetic field is applied to it from an externally located bias magnetic field-applying layer to keep the linearity of its characteristics. With a part of the bias layer flipped over, however, the bias magnetic field wanes resulting in the inability to give a good enough bias magnetic field to the magneto-resistive effect device: this could render the MR characteristics nonlinear.
In another possible deterioration model (2), there would be a phenomenon occurring, in which the pin direction of a pinned layer that is a so-called fixed magnetization layer is off normal.
One possible way of fixing up such deterioration models (1) and (2) is to fix up the deterioration by the application of a high magnetic field of a few KOe (oersteds). However, much difficulty would be encountered in the incorporation in common hard disk systems of a mechanism that generates a fixing magnetic field. Further, the application of a high magnetic field of a few KOe (oersteds) may possibly have adverse influences on the stability and reliability of operation of the device.
The situations being like this, the invention has been made for the purpose of a novel yet very effective method of fixing up a deteriorated site in the magneto-resistive effect device (reproducing device) in a thin-film magnetic head caused by the so-called thermal asperity occurring as a hard disk system is in operation, while that device remains incorporated in the hard disk system without dismantling it.
It is here noted that the prior art that would seem pertinent to the invention of this application is JP(A) 2001-67619. This prior art comes up with a method in which, before a ferromagnetic tunnel junction device is actually in use, a current is passed through it for a given time in a high-temperature atmosphere, thereby stabilizing the resistance value of an insulating film during actual use. This prior art shows operation implemented before actual use. By contrast, the invention of this application is directed to fixing operation that is implemented when device malfunction is found after it has been actually in use while remaining incorporated in a hard disk system: it is quite different in construction and advantages from that prior art.